Exhaust gas re-circulation is a technique commonly used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. This technique has proven particularly useful in internal combustion engines used in motor vehicles such as passenger cars, light duty trucks, and other on-road motor equipment. The exhaust gas re-circulation technique primarily involves the re-circulation of exhaust gas by-products into the intake air supply of the internal combustion engine. This exhaust gas thus reintroduced to the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxide. Furthermore, the exhaust gases typically contain a portion of unburned hydrocarbon which is burned on its reintroduction into the engine cylinder, which further reduces the emission of exhaust gas by-products which would be emitted as undesirable pollutants from the internal combustion engine.
However, it is necessary to carefully control the proportion of re-circulated exhaust gas to intake air. For example, while a greater proportion of exhaust gas may be re-circulated at low load levels, it is necessary to ensure that the proportion of re-circulated exhaust gas does not become excessive, causing the engine to stop due to a lack of sufficient oxygen to mix with the fuel so as to permit combustion. On the other hand, if the proportion of exhaust gas re-circulated at full engine load is excessive, the power output of the internal combustion engine is reduced, and the engine will typically emit undesirable quantities of smoke and particulate matter due to unsatisfactory combustion in the engine cylinders. Therefore, it is clear that the exhaust gas re-circulation process is desirably tightly controlled.
Another technique useful in the control and reduction of undesirable emissions from internal combustion engines is the use of pressure-charged intake air. This permits the use of relatively smaller cubic displacement and lighter weight internal combustion engines in mobile equipment, reducing in turn the specific fuel consumption of the vehicle and overall mass of the vehicle necessary to perform a given function. In addition to the benefits of reduced size and mass, the typical pressure-charging device may be controlled to provide improved emissions characteristics. Pressure-charging machines suitable for such applications include the exhaust gas driven turbocharger which is comprised typically of an exhaust gas driven turbine linked to a compressor disposed in the intake air stream to provide compression of the intake air. One way of controlling a turbocharger is to provide a gate which controls exhaust gas flow and gates exhaust gas to bypass the exhaust gas turbine and control the charging rate of the turbocharger so that the maximum pressure limits of the associated internal combustion engine are not exceeded. Another device particularly suited for such pressure-charged internal combustion engines is the gas-dynamic pressure-wave supercharger. This pressure-wave supercharger is particularly well suited for use in diesel-type internal combustion engines for such applications, due to the fact that this type of supercharger provides a rapid response to changing load requirements and provides a high charging rate in the lower and middle ranges of operating speeds. Furthermore, since the exhaust gas and the intake air are in direct contact in such a machine, there is a degree of mixing therebetween which desirably varies according to the load placed on the internal combustion engine apparatus. For example, at full load the supercharger is typically over-scavenged to the point where a greater amount of air is compressed and is available to the engine than is required, permitting a complete scavenging of the exhaust gas from the supercharger. However, at less than full load and as the load decreases, the amount of available intake air likewise decreases so that at low and partial loads the supercharger is under-scavenged and permits a portion of the exhaust gas to be fed to the internal combustion engine along with the intake air. This characteristic is generally desirable and works in conjunction with the emission controls of the internal combustion engines. It is typically insufficient to provide an adequate control of emissions as the legal standards and emissions standards are progressively tightened to permit reduced vehicle emissions. Furthermore, the uncontrolled re-circulation of exhaust gas into the compressed intake air via the supercharger can adversely affect the operation of the internal combustion engine at low speed and low load conditions such as idling.
One means of controlling the scavenging of exhaust gas by-products from the supercharger is the provision of a gas pocket in the gas casing between the high pressure exhaust gas duct and the low pressure exhaust gas duct. This is typically done in conjunction with an expansion pocket provided in the air side casing of the supercharger to improve control of the low pressure scavenging of the expanded exhaust gas from the supercharger rotor. It is of course possible to provide and uncontrolled flow of exhaust gas to the gas pocket. As the static pressure in the gas pocket is the same as the pressure in the exhaust gas duct, this is called a static gas pocket feed. A variable gas pocket is another and better method of providing exhaust gas to the gas pocket by way of a passage from the exhaust gas duct wherein a valve is provided in the passage to provide a controllable flow of the exhaust gas to the gas pocket.
One method of controlling the operation of the valve in such a variable gas pocket apparatus is by way of a temperature-responsive bimetal flap. The flap operates in response to increasing exhaust gas temperature to progressively close and decrease the flow of exhaust gas into the gas pocket. Therefore, as the load on the internal combustion engine increases and the exhaust temperature rises, the amount of exhaust gas provided to the gas pocket is progressively reduced, and the amount of exhaust gas energy available for operating the supercharger rotor is progressively increased. Since the supercharger in this situation is progressively tending toward the high load, over-scavenged condition, the scavenging effect of the gas pocket is neither required nor desired.
It is also known to provide a valve for the gas pocket which is operated by an actuator responsive to a controller for operating the motor to provide valve positions at various engine operating and load parameters as selected according to pre-determined characteristic curves. As the legal emission standards have become more stringent, however, it has become increasingly desirable to integrate the control functions of the engine with the emission control system to ensure smooth operation of the engine while providing the minimum emissions therefrom. One of the primary disadvantages in obtaining this goal in the related art has been the inability to integrate the control of multiple engine functions, for example, the rate of fuel injection into a diesel-type engine, control of the intake throttle valve for dividing the nominal air flow in the intake air ducting to the supercharger, providing desirable control of the variable gas pocket, and providing a simultaneous integrated control of such functions while providing a closed-type control loop to ensure the best possible engine and emissions performance. The present invention overcomes some of these related art disadvantages.